As the crushing apparatus, a self-propelled crushing machine can be exemplified (see Patent document 1, for instance). As shown in FIG. 18, the crushing machine includes a rotary crusher (crushing unit) 151 and a tub (rotary tub) 152 for feeding the rotary crusher 151 with wood (object to be crushed) that rotates around an independent shaft center. Incidentally, the tub 152 and the crusher 151 or the like are provided to a machine frame 153, and a traveling unit 154 is also provided to the machine frame 153. The wood (object to be crushed) is put into the tub 152 and crushed by the crusher 151, and the crushed articles are fed down below the crusher 151 to be discharged outward by a transport conveyor 155.
The wood as the object to be crushed often includes a tree branch, trunk, stump or the like and the hardness, size or the like thereof often varies, so that the crusher 151 may go in an overloaded state with some kinds of the object to be crushed and often stop, where the operating efficiency may be decreased.
In a wood-crushing machine according to the Patent document 1, a target crushing rotation speed by the crusher 151 is set, and when the actual rotation speed of the crusher 151 is higher than the target crushing rotation speed, the tub 152 is rotated in a forward direction at a predetermined rotation speed.
When the actual rotation speed of the crusher 151 is lower than the target crushing rotation speed but higher than a reference rotation speed that is lower than the target crushing rotation speed, the rotation speed of the tub 152 is gradually decreased from the predetermined rotation speed in the forward direction. And when the actual rotation speed of the crusher 151 is equal to or lower than the reference rotation speed, the tub 152 is stopped or rotated in the reverse direction.
Accordingly, it is prevented that too much objects to be crushed are fed to the crusher 151, thereby avoiding that the crusher goes in the overloaded state.
Patent document 1: Japanese Patent No. 3298829 (Pages 3 to 6, FIGS. 1, 3, 4, and 5)